In an ink-jet printer, droplets of ink or colorant are ejected through orifices and onto a printing medium in a two-dimensional pixel array to form an image. In a multi-pass print mode, the printhead may eject droplets from certain of the orifices on a given pass and from certain of the other orifices on subsequent or earlier passes. The overall pattern, size, timing and spacing of individual ink droplets or drops ejected from the ink-jet printer and printed within a given area of the media can affect the print quality of the image.
Print masks may be generated for given printheads operating in given print modes to control the particular pass of a multi-pass printmode in which a particular orifice corresponding to a particular pixel or cell in the image will be ejected. The print mask may be represented by an array of numbers, each one over a pixel, that represents the number of the pass (for example 1 through 8 in an 8-pass printmode) in which that pixel will be printed. In a dither mask, each value in the print mask represents a discriminator against which input levels are to be tested. Print masks can be generated incrementally using a matrix-based masking process which is based on various spatial and temporal constraints. Commonly assigned U.S. Pat. No. 6,542,258, for example, describes using a constraint matrix to generate a print mask.
Some printheads create characteristic “satellite” droplets which land in a consistent relation to the main drop being ejected. Satellite droplets may adversely affect image quality. Although the image effects due to a satellite may be less noticeable where the number of passes is high, in the case of print modes with fewer passes, the effects may be increased. In addition, where the size of satellite drop is large with respect to the main drop, the effects of satellite drops may be more visible.